Insulating compound



' 1,638,557 1927' J. M. WILSON msumwme comrouun Filed July so, 1924hrm/orr JM/Ml W/Zm/Z Patented Aug. 9, 1927.

UNITED STATES v 1,638,557 PATENT OFFICE.

JOHN 1!. WILSON, F BRONX, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COM-PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

INSULATING COMPOUND.

Application filed July 30,

This invention relates to insulating compounds and specifically toelectric insulating cements.

An object of the invention is to produce 5 an insulating cement whichwill be efficient under severe conditions of service.

Insulating cements used for insulation between metallic elements inlightning arresters and the like in telephone or other circuitsfrequently deteriorate with time in service to such an extent as tocause exces sive current leakage which results in objectionabletransmission losses. Investigation has shown that such deterioration isoften caused by freealkali or alkali-producing materials in theinsulating cement which in the presence of moisture soon form leakagepaths for the current.

The cement of the invention comprises materials as low in free alkali oralkali-producin materials as porcelain and having high insulationproperties. Preferably, the cement comprises ground porcelain as afiller, a shellac as a bindingmaterial and an easily vaporizablematerial, such as alcohol, as a solvent for the shellac. From thesematerials'combined in suitable. proportions an insulating cement hasbeen produced which will retain its insulation properties over longperiods of time and under extreme conditions of service.

The invention will be clear from the following detailed description readin connection with the accompanying drawing:

The single figure shows a sectional view of a spark-gap arrester' of awell known grounded by being held in position against the metal strip 3which is connected to ground through a binding post,not shown. The outerblocks 2 are held in place by contact springs 4 which extend through theporcelain base 5 and connect the blocks 2 to opposite sides of the linethrough the binding posts 6. A slight air-gap 7 is maintained betweeneach carbon block 2 and the ground- 56 ed block 1 which it faces bystrips of mica 1924. Serialno. 729,041.

not shown. Potentials exceeding a certain value, due to lightning orother causes, will jump across the air-gaps 7 from line to ground thusdissipating any static charge which may accumulate on the line due tothe excessive potential. A recess in the lower part of the porcelainbase 5is filled with the insulating cement 8 of the invention toinsulate the two sides of the line from each other, from ground, andfrom the support on which the porcelain base 5 will rest. It has beenfound that with the insulating cement of the invention, the insulationin such a device as described will function satisfactorily for thelifetime of the device and under severe conditions of service.

As stated above the cement of the invention is made from a. bindingmaterial, such as shellac, a vaporizable solvent such as alcohol, and afiller, such as ground porcelain.

Any other materials having a degree of alkalinity not exceeding that ofground porcelain may be used in place of ground porcelain as a filler inthe cement if they have the required insulation properties and aremechanicall suited for the purpose. Materials whic have been found to besatisfactory are certain grades of silica, such as New JerseyPulverizing Companys extra quality silica infusorial earth, such asElmer and Amends technical I infusorial earth, sand, such as Ottawasand, and Cellite Producing Companys Sil-o-Cel.

The amount of shellac and alcohol to be used in the insulating cement ofthe invention will vary with the fineness of the filler. It is, ofcourse, preferable to use a minimum of shellac so that the drying of thecement will not be retarded objectionably. The alcohol is used merely asa solvent and, of 05 course, must be used in such proportions as toinsure complete volatilization in order that the final cement will havesufficiently good electrical and mechanical properties. The fineness ofthe filler should be governed 100 by its mechanical suitability for theproposed use as the degree of fineness is not important from anengineering standpoint provided the material is coarser than 50 mesh.Preferable roportions to be used in the 105 making of t e insulatingcement in accordance with the invention are approximately by weight 80per cent filler, having a fineness of 100 mesh or above, 10 per centshellac and 10 per cent alcohol. It has been 110 found that a cementmade from the above mentioned materials in approximately the proportionsspecified may be applied be-,

tween the elements to be insulated from each otherwithout the use ofheat, and after a comparatively short exposure to the atmosphere willproduce a material which in addition to its exceptionable insulatingproperties, has satisfactory adhesive qualities, and is substantiallynon-hygroscopic and non-flammable.

Although the invention has been described and illustrated in connectionwith its use as a sealing compound in lightning arresters,

'it is to be understood that it is not limited to such use but iscapable of general application wherever good insulatlon properties arere uiredL, For example, it may be usedhave a sufiiciently low degree ofalkalinity and have the required adhesive insulation or solventualit-ies.

What 1s claimed is:

1. An insulatin cement comprising by weight substantial y 10 per centalcohol, 10 per cent shellac, and 80 per cent pulverized filler having adegree of alkalinity comparable to that of porcelain and low electricalconductivity.

2. An insulating cement comprising, shellac, an easily vaporizablesolvent therefor and a pulverized filler having a degree of alkalinityat least as low as porcelain and having high insulation properties, saidshellac and said filler being combined in the proportions ofsubstantially one to eight, respectively.

- 3. An insulating cement comprising alcohol, shellac and substantially80 per cent of ground porcelain. g

In Witness whereof, I hereunto subscribe my name this 28th day of July,A. D., 1924. JOHN M. WILSON.

